Thermal actuators are devices that convert thermal energy into mechanical energy. In some applications, the thermal energy is actively provided to the thermal actuator, for example by an electrical heating element, in which case the actuator is commonly referred to as an ‘electrothermal’ actuator. In this case, conversion of thermal energy into mechanical energy is a primary function of the thermal actuator.
In other applications, the thermal energy is provided by the surroundings of the actuator, sometimes referred to as a ‘passive’ system. In this case, the actuator acts as a temperature sensor as well as a means of converting thermal energy into mechanical energy. In some of these applications the actuator is commonly referred to as a ‘thermostatic actuator’.
In many of these ‘passive’ applications, the actuating force is used to operate a valve, wherein the valve responds to a change in temperature of the surroundings of the actuator by closing, completely or partially, a flow through the valve, or, in the case of a three-way valve, by directing the flow in one direction or the other.
There are many known types of thermal actuators, however they have in common that the thermal energy is converted into mechanical energy by expansion of a material within the actuator. This expansion may be related to a phase transition of the material at a given temperature or within a given temperature range, or it may be related to thermal expansion of a material within a certain phase over a certain temperature range.
Although existing ‘passive’ thermal actuators can act as sensors by comparing the temperature of their surroundings to a preset temperature (or temperature range), they cannot actuate based on temperature differences between different sections of the same actuator. As such, there is a need for technological advancement.